One of our ducklings (now 10 days old) is vomiting white/milky liquid. It's not a lot, but less than a half teaspoon. Is this something to be concerned about? They are generally on starter duckling feed, have the occasional lettuce, and had some peas the other day. All with plenty of water. One did grab and eat a little bit of newspaper before we could stop it, but we can't tell if that's the one that's tossing up the liquid.